1. Field of the Invention
This invention relates to sliding clasp fasteners and more particularly improvements in a slide fastener stringer having a discrete formation of coupling elements or scoops mounted on a support tape. A series of such scoops are formed on the tape by injection or extrusion molding of a plastic material.
2. Prior Art
It has heretofore been proposed to use synthetic resins as the material for forming fastener coupling elements for reasons of fashionability and physical feel unavailable from metallic materials. Certain types of plastic material such as for example polyacetal have also been preferred for their physical strength comparable to metals. However, polyacetal is rather weak in its resistance to shock, and fastener elements made thereof are prone to be brittle when applied to slide fasteners used on bags, outdoor canvas and other articles that are handled in a rough manner. Nylon has been proposed as a substitute for polyacetal as it is much stronger in shock-resistance. However, due to its softness, nylon fastener elements do not have a satisfactory anchoring strength at the fastener tape and would often tend to spread apart at their leg portions when the fastener tape was soaked wet and swollen. To eliminate this problem, means have been considered to interconnect the two oppositely disposed legs of the element by a suitable connecting strip provided in an opening in the tape, the opening being formed by punching, cutting or by a piercing pin. However, due to the limitation imposed on the size of such an opening and hence the size of the connecting strip, the fastener elements were liable to spread apart along their superposed legs or otherwise move out of place when the fastener tape was wetted and swollen, resulting in sluggish or otherwise inoperative manipulation of the slider. This tendency is pronounced when the bead on the edge of the tape is increased in size to strengthen resistance to lateral pull.